Impulse resistance welder



May 16, 195o Filed Dec. 23, 1942 H. KLEMPERE R 2,508,115

IMPULSE RESISTANCE WELDER 2 Sheets-Sheerl l /N VEN-roe. //vs LEMPERE,

Patented May 16, 1950 UNITED STATES PATENT OFFICE IMPULSE RESISTANCE WELDER Hans Klemperer, Belmont, Mass., assignor to' Raytheon Manufacturing Company, Newton, Mass., a corporation of Delaware Application December 23, 1942, Serial No. 469,863

(Cl. 21S-4) 22 Claims.

Fig. 1 is a diagrammatic sketch of a system embodying my invention;

Fig. 2 is a pair of curves illustrating the mode of operation of the system shown in Fig. 1; and

Fig. 3 is a set of curves illustrating the relationships between the various currents and voltenergy is supplied to effect the actual welding operation i. e., the fusion of the two or more parts of the work together, and this last period may, if desired be followed by a subsequent period during ywhich additional energy is supplied to the work for annealing purposes. of the present application it will be understood that the term welding operation refers to the fusion of the work and is considered independent of such other operations which may be added or omitted as desired to eifect the complete welding cycle.

Heretofore pulses of current derived from a commercial line frequency source, such as a sixty-cycle source, were utilized for welding purposes. determined number of cycles or half cycles of current. However, the use of current pulses of this kind resulted in various drawbacks. In order to transform the current at the standard commercial frequency, relatively large sizes of transformer were necessary. It was also necessary to draw all of the power from the single phase line instead of the more desirable practice of drawing a balanced load from a three-phase line. In an attempt to increase the power supplied to the welding load, the secondary voltage of the welding transformer was raised to undesirable high values. Such previous systems also have been relatively inflexible, and thus not adaptable to a wide variety of welding loads.

An object of this invention is to decrease the size of the welding transformer and associated parts.

A further object is to provide for increased flexibility in the adjustment of a welding sys tem of the foregoing type.

A still further object is to enable balanced loads to be drawn from a three-phase or other plural-phase line with a Welding system of the above type.

The foregoing and other objects of this invention will be best understood from the following description of an exempliflcation thereof, reference being had to the accompanying drawings, `wherein:

For the purposes Such pulses usually consisted of a preages occurring in the arrangement of Fig. 1 during the operation thereof.

The system illustrated in Fig. 1 comprises a welding load i which may either be of the ordinary spot resistance welding type, but is preferably a seam welding load. The resistance welding load I is supplied with welding current from the secondary 2 of a welding transformer 3 whose primary 4 is adapted to be supplied with the del sired pulses of current from a condenser 5. The

condenser 5 is charged to the desired voltage from a suitable source of direct current, such asa series of grid-controlled rectifier tubes 6. The tubes 6 may be arranged in a full-wave rectifying system energized from a three-phase transformer 'l having a pair of secondary windings 8, each arranged in a star connection. The transformer 'i also has a primary winding 9 arranged preferably in a delta connection and energized from a suitable three-phase source of alternating current. The neutral points of the two secondary windings 8 are interconnected by an interphase reactor It from the center point of which extends the negative lead II of the rectified current supply. The outer end of each coil of the secondary windings B is connected to one of the anodes of one of the rectifiers 6. The cathodes of the rectiers 6 are all connected to the positive lead I2 of the rectified current supply. The condenser 5 is connected between the positive and negative leads Il and I2 so as to become charged by the rectied current supplied thereto.

In order to control the voltage delivered by the rectifier 6, each grid of these rectiers is connected through a high resistance I3 to a grid control lead I4. One of the grids may have a source of alternating current I5 connected in series with the resistance I3 so as to cause said rectier tube to supply a final trickle charge to the condenser I5 as it approaches the desired nal value of voltage thereon. This operation is described more fully and claimed in the copending application of John W. Dawson, Serial No. 312,712, filed January 6, 1940, now Patent No. 2,483,691, dated October 4, 1949. The voltage which is supplied to the grid control lead I4 is derived from a potentiometer I6 connected across the condenser 5. A glow discharge tube I'l in series with a resistance I8 is connected from an adjustable point I9 on the potentiometer I6 to the positive or cathode lead l2. The voltage across the resistance I8 is connected by means of a conductor 25 to the grid control lead I4.

As the voltage on the condenser rises, the voltage applied to the glow tube I reaches a point at which that glow tube starts to conduct current. Thereafter the voltage across the glow tube remains constant, but the voltage across the resistance i8 rises linearly with respect to the voltage at the point i9, and thus the voltage across the resistance i8 responds to the voltage on the condenser 5. When the desired Voltage is attained across the condenser 5, the grid control lead I4 supplies a sufficiently negative voltage to the grids of the tubes 9 so as to cause said tubes to become extinguished. Due to the presence of the alternating voltage l5 in the grid lead of one of the tubes 5, that tube continues to rire in delayed phase, the angle of which increases and thus causes the tube to supply smaller increments or" charging current to the condenser 5. When the condenser reaches its final Value, the voltage supplied by the grid control lead i4 is sumcient to extinguish the last tube 6. However, this tube with the alternating voltage superimposed on its grid acts as a trickle charger whenever the charge on the condenser 5 leaks off to a sucient degree to require such a trickle charge supply. A voltmeter 2i may be connected across the condenser 5, if desired. The operation of the glow tube l1 and its associated control circuit is described more fully and claimed in my copending application, Serial No. 461,571, filed October 10, 1942, now Patent No, 2,383,492, dated August 28, 1945.

In order to discharge the condenser 5 into the resistance welding load, a controlled discharge tube 22 is connected between the negative side of the condenser 5 and one end of the primary winding it, the positive side of the condenser 5 being connected directly to the other end of said primary winding. The tube 22 is preferably of the type having a mercury pool cathode 23, an anode 24, and an igniting electrode 25 which when supplied with a pulse of igniting current initiates an arc spot on the surface of the mercury pool 23. In order to supply igniting impulses to the igniting electrode 25, there is provided an impulse generator 26. This may be a standard impulse genera tor employing a tetrode such as of the present 2950 type. This generator is adjustable to allow a variation in the number of impulses which it supplies per second. In a particular embodiment of my invention I utilized an impulse generatoi1 which supplied impulses which could be adjusted in frequency from rive to twenty impulses per second. The impulsesdelivered by the generator 25 are preferably amplied by an impulse amplifier 2. Both the generator '26 and the amplifier 2i may be energized from a suitable source of alternating current 28. In order to control the number of impulses which are delivered to the tube 22 during a single welding operation, an automatic time delay relay 29 is utilized. This relay closes a controlling circuit for the impulse generator 26, causing that generator to operate for a suicient period of time for a welding operation to be completed, whereupon the relay 29 opens the control circuit for a sufficient waiting time until the next welding operation is to be initiated. The relay 29 may be adjustable so as to provide for a varying period of time during which the impulse generator is maintained in operation. Of course the generator 26, the amplifier 21, and the time delay relay 29 are all standard pieces of apparatus so that it is not necessary to include further details thereof in this application.

Each time an igniting impulse is supplied to the igniting electrode 25, a discharge is initiated in the tube 22 and the condenser 5 discharges into the primary Winding 4. It is desirable to use a pickup circuit consisting of a condenser 30 in series with a resistance 3l across the tube 22 so as to assist in the reliable initiation of a discharge lin the tube 22 each time an igniting impulse is supplied to the electrode 25.

The operation of the system each time an igniting impulse-is supplied to the tube 22 may be understood more readily with reference to Fig. 2, in which the curve E represents the Voltage on the condenser 5 and the curve I represents the welding current, both curves being plotted along a horizontal time axis. At the time To the condenser' 5 is assumed to be fully charged, and an igniting impulse is supplied to the electrode 25. Thereupon the tube 22 starts to conduct current and the voltage E drops to zero at the time T1, While the current I rises to a maximum value at that time. During the time To-Ti ilux was being built up in the transformer 3 so that, after the time T1, the collapse of the ux causes the current to continue flowing in the Same direction, although decreasing in magnitude, and thus to recharge the condenser 5 to an inverse value, which reaches a maximum at the time T2, at which time the current I falls to zero. The voltage on the condenser 5 at the time T2 would tend to discharge back through the primary winding 4, causing a reversal of current to take place. However, the tube 22 being a rectier cannot carry such a reversed current flow. If the current ow terminated at the time T2, the inverse voltage would be trapped on the condenser 5 in a direction which would not be useful for welding purposes.

In order to permit the inverse current flow, an additional controlled tube 32 is connected across the tube 22. The tube 32 likewise is preferably of the type having a mercury pool cathode 33, an anode 34, and an igniting electrode 35 which is adapted to initiate au arc spot on the surface of the pool 33 when supplied with an igniting impulse. The igniting impulse is supplied to the electrode 35 by having that electrode connected through a controlled discharge tube 36 in series with a resistance 31 to the anode 34. The controlled tube 36 may have its grid connected through a resistance to its anode, thus forming essentially a rectier in series with the igniting electrode 35, of such a polarity as to deliver a pulse of current to the electrode 35 when the anode 34 of that tube becomes suiciently positive. At the time T2 the voltage across the rectifier 22 reverses, and thus likewise the voltage across the tube 32 reverses. Upon such reversal of voltage, the tube 36 conducts current, supplying an igniting impulse to the electrode 35, and thus causing the tube 32 to start conducting current. This permits the inverse pulse of current, as shown in Fig. 2, in

the time interval T2-T4 to flow. Thus the condenser 5 discharges back through the primary winding 4 so that at the time T3 its voltage has again fallen to zero. However, due to the inductive action of the transformer 3, the-current continues to flow, falling to zero at the time T4, at which time the condenser has re-gained a charge which, however, in this case is in the same direction as the initial charge and is thus available to assist in the subsequent welding operation. Since at the time T4 the current falls to zero, the tube 32 becomes extinguished, and in absence of another igniting impulse supplied to the electrode 25, the tube 22 does not re-ignite, and therefore the current pulse is completed at the time T4. Sometime thereafter the rectiers 5 again supply charging current to the condenser 5 which builds up its voltage from the value which it possesses at the time T4 to the original fully charged value necessary for the production of a subsequent welding operation.

It is, of course, desirable that the rectiiiers 6 do not attempt to supply charging current to the condenser 5 during the time it is supplying a welding current impulse. For this purpose a hold-off circuit is utilized comprising a rectifier tube 31' connected in series with a resistance 40 and a condenser 4I across the primary winding 4. The rectifier tube 31 has a cathode 38 preferably of the constantly energized type, such as a heated filament, connected to the end of the primary winding 4 to which the anode 2:1 of the tube 22 is connected. The tube 3l also has an anode 39 which is connected to the resistance 40. A conductor 42 connects the point intermediate the anode 39 and the resistance 40 to the grid control lead I4. When the tube 22 is ignited, the main discharge circuit is completed and supplies the voltage of the condenser 5 across the primary winding Il. This voltage is likewise connected across the hold-off circuit. The rectifier 31 is of such a polarity as to pass charging current to the condenser 4I which quickly becomes charged to the voltage of the condenser 5. It will be seen that under these conditions the lower plate of the condenser 4l is made positive while the upper plate becomes negative. This negative voltage is impressed by the conductor 42 to the grid lead I4, and thus holds off all of the rectiflers 6 from further conduction of current as long as this hold-off voltage is present. As the voltage on the condenser 5 decreases and reverses, the condenser 4I cannot discharge through the tube 31', due to its rectifying action. Therefore the condenser 4I can only lose its charge by a leakage discharge path provided by the resistance 40, conductors 42 and 20, yand resistance I8. This discharge circuit has a sufficiently long time constant so that the negative hold-off voltage is maintained on the grids of the tubes t until a sunicient period of time after the completion of such a welding current impulse as is illustrated in Fig. 2. The operation of such a hold-off circuit is more fully described and claimed in my copending application, Serial No. 434,670, filed March 14, 1942.

In Fig. 3 I have illustrated the sequence of operations which occur in a practical embodiment of the arrangement as illustrated in Fig. 1. In Fig. 3, a illustrates the welding current impulses, b illustrates the variation is in condenser voltage, c shows the pulses of charging current supplied to the condenser 5, and d shows the igniting impulses which are supplied to the igniting electrode 25 of the tube 22.

As will be seen from the curve a, the frequency of each welding current impulse is determined solely by the circuit constants of the condenser discharge and welding circuit. Thus we see that the frequency of each of these welding current impulses is independent of any line frequency and is solely dependent upon the circuit constants as above described. By adjusting these constants the frequency may be adjusted. Likewise it will be seen that since the frequency of each current impulse is fixed by the circuit constants of the welding load, the current is supplied to that load with maximum effectiveness. I prefer to use frequencies for each welding current impulse substantially higher than that of ordinary commercial line frequencies, and more particularly of the order of about 200 cycles per second or more. The curve d shows that the number of impulses of welding current supplied during any welding period is independently controlled by the frequency of the impulse generator. At the time To, indicated in Fig. 3, the relay 29 closes the circuit to the impulse gen erator 26, thus initiating the welding period. At the time T1, likewise represented in Fig. 3, the relay 29 opens the control circuit to the impulse generator 26, thus terminating the Welding period. Thus by adjusting the frequency of the impulse generator 26, the number of welding current impulses supplied during the welding period can be readily selected. Likewise by adjusting the time during which the relay 2B maintains the control contacts closed, the length of the welding period can be adjusted. It will be readily seen that the system which I have illustrated affords a wide variety of adjustments making for a very flexible and adaptable system.

Due to the adaptability of the system described above, it is particularly adaptable for use in portable welding machines capable of welding alloy steel and light gau-ge aluminum. The frequency of about 200 cycles or more which is supplied to the primary winding 4 allows a considerable decrease in the transformer size. In a practical instance I have found that the requisite power can be supplied to the welding load with a smallsized transformer and with a low secondary voltage of about 60 volts, thus eliminating the necessity for using excessively high voltages which the art had previously been compelled to use. Of course, due to the storage aspect of the condenser 5, the load which is drawn from the power lines is equally distributed over the three-phase line which, as previously described herein, is a desirable mode of operation. Since the power which is supplied for a single welding operation is subdivided into separate discrete impulses, each impulse being stored in a condenser, by making each impulse shorter in duration, the peak power which can be supplied to the welding load is greatly amplified, although the total power during a single welding operation may remain at a relatively low level. In many types of welding operation high "power peaks of the foregoing type are very desirable, and produce greatly improved welds.

In one embodiment of my invention I used a. welding transformer with a ratio of transformation of fifty to one. The capacity of the condenser 5 was about 600 mid., while the inductance of its associated discharge circuit was 0.6 microhenry. The voltage to which the condenser 5 was charged was approximately 3000 volts, and with the above ratio of transformation, the secondary welding transformer voltage did not exceed 60 volts. With above constants of capacity and induetanee, the natural frequency of each welding impulse was about 165 cycles per second. The secondary welding current peak was about amperes maximum. The welding transformer had about one hundred fifty primary and three secondary turns. The core material was of a special magnetic alloy known as hypersiL utilizing 120,000 flux lines per square inch and 7 givinga-.resultant total Viiux of about12i00 kilolines- `maximum, lwithout saturation .and Ausing only twenty square `inches cross-section of transformer core.

Orf .course it is to be understood that this invention is not limited to the particular details. as described above as many 4equivalents will suggest themselves to those skilled in the art. It is accordingly desired that the appended claims be given a broad interpretation confimensurate with the scope of the invention within. the art.

' What is claimed is:

l. Awelding system comprising a condenser, meansv for charging said condenser, a resistance welding load, means for discharging said condenser into said `wel ing load by an oscillating discharge whose frequency is determined primarily by the condenser and its associated discharge circuit, said last-named means limiting said discharge to substantially a -single oscillation, and means for operating said discharging means a plurality of times ior producing a single welding operation.

Y2. A welding system comprising a condenser, means for charging said condenser, a. resistance welding load, means for dischargingsalid condenser into said welding load by an oscillating discharge whose frequency is determined primarily by the condenser and its associated discharge circuit, said last-named means limiting said discharge to substantially a single oscillation, and means for operating said discharging means a plurality of times for producing a single Welding operation, the frequency of the repetition vof operation of said discharge means being substantially lower than the frequency of said current impulses themselves.

3. A system comprising a condenser, means for charging said condenser, a load, a controlled rectifying tube connected in series between said condenser and said load for discharging said condenser into said load by an oscillating discharge Whose frequency is determined primarily by the condenser and its associated discharge circuit, said tube being of the type which conducts for a single conducting period `upon the supply of an igniting impulse thereto, and a second rectifying discharge tube connected with inverse polarity across said first-mentioned tube, said second tube beingy arranged to conduct whenever a substantial voltage is applied thereto in the conducting direction.

4. A Welding system comprising a condenser, means for charging said condenser, a resistance welding load, a controlled rectiiying tube connected in series between said condenser and said welding load for discharging said condenser into said welding load by an oscillating discharge whose frequency'is determined primarily by the condenser `and its associated discharge circuit, said tube being of the type which conducts for a single conducting period upon the supply of an igniting impulse thereto, asecond rectifying discharge tube connected with inverse polarity across said first-mentioned tube, said second tube being arranged to conduct Whenevera substantial voltage is applied thereto in the conducting direction, and means for supp-lying a plurality of spaced igniting impulses to said first tube for producing a plurality oi discharges from said condenser during a single welding operation.

5. A welding system comprising a condenser, means for charging said condenser, a resistance welding load, a controlled rectifying tube connected in series between said condenser and said Welding load for discharging said condenser into said `welding :load by an oscillating discharge whoseA frequency is determined primarily by the condenser and its associated discharge circuit, said tube being ofthe type which conducts for a single conducting period upon the supply ofv an igniting limpulse thereto, a second rectifying-discharge vtube connected vwith inverse polarity across said first-mentioned tube, said second tube being arranged toconduct whenever a substantial .voltage is applied thereto in the conducting direction, and means for supplying a plurality of spaced igniting impulses to said first tube for producing afplurality of discharges from said condenser. during a single Welding operation, the frequency of the repetition of said last-named means being substantially lower than the frequency of said current impulses themselves.

6. A welding system comprising a condenser, means for charging said condenser, a resistance welding load, means for discharging said condenser into said welding load by an oscillating discharge whose frequency is determined primarily by the condenser and its associated discharge circuit, said last-named means limiting said discharge to substantially a single oscillation, means for operating said discharging means a plurality of times for producing a single welding operation, and means for preventing said charging meansfrom supplying charging current vto said condenser during each of said discharge oscillations.

7. 'A welding system comprising a condenser, means for charging said condenser, a resistance welding load, means for discharging said condenser' into said welding load by an oscillating discharge whose frequency is determined primarily by the condenser and its associated discharge circuit, saidlast-named means limiting said discharge to substantially a single oscillation, means for operating said discharging means a plurality of times for producing a single Welding operation, and means for varying the frequency of operation of said last-named means.

8. A welding system comprising a condenser, meansvfor charging said condenser, a resistance welding load, a controlled rectifying tube connected in seri-es between said condenser and said welding load for discharging said condenser into said welding load by an oscillating discharge whose frequency is determined primarily by the condenser and its associated discharge circuit, said tube being of the type which conducts for a single conducting period upon the supply of an igniting impulse thereto, a second rectifying discharge tube connected with inverse polarity across said rst-mentioned tube, said second tube 4being, arranged to conductvwhenever a substantial voltage is applied thereto in the conducting directionand means for supplying a plurality of .regularly spaced ignition impulses to said inst-mentioned tube to discharge said condenser a plurality of times during a single welding operation, and means for recharging said condenser to substantially the same potential ,between each discharge thereof.

9. A system comprising a condenser, unidirectional voltage means successively charging said condenser with the same polarity for each of said charges, a load circuit, -a controlled rectifier tube connected in series between said condenser and saidload circuit for discharging said condenser into said load by an oscillating discharge Whose frequency is determined primarily by the capacitance of said condenser and the inductance of its associated discharge circuit, saidv tube yheinz oi the type which conducts for a single conducting period upon the supply of an igniting impulse thereto,va second rectifying discharge tube connected with inverse polarity across said iirstmentioned tube, said second tube being arranged to conduct whenever a substantial voltage is applied thereto in the conducting direction, and

means for supplying an ignting impulse to said first-named tube following each of said charges, the constants of said condenser and its associated discharge circuit being related so that the period of said oscillating discharge is substantially less than the interval betweensuccessive igniting impulses.

10. In combination, a capacitor, means adapted to function as a source of periodically pulsating potential in circuit with said capacitor for supplying charging current thereto, electric discharge valve means of the arc-like type interposed between said source and capacitor for controlling the supply of charging current to said capacitor, a control circuit connected to said valve means and arranged to render said valve means conductive when a potential greater than .a predetermined critical value is impressed therein in a positive pulsation of said source, and means adapted to impress in said control circuit a second periodic potential of the same periodicity as said source potential and having a sloping wave front superimposed on a third potential which gradually decreases as the capacitor potential increases above a preselected magnitude, the magnitude of said second and third potentials being such that the resultant potential in said control circuit first rises above said critical value at substantially the same instant early in each positive pulsation while said capacitor potential is below said preselected magnitude and at an instant gradually later in each succeeding positive pulsation as said third ptential decreases.

l1. In combination, a capacitor, means adapted to function as a source of periodically pulsating potential in circuit with said capacitor for supplying charging current thereto, electric discharge valve means of the arc-like type interposed between said source and capacitor for controlling the supply of charging current to said capacitor, a control circuit connected to said valve means and arranged to render said valve means conductive when a potential greater than a predetermined critical value is impressed therein in a positive pulsation of said source, and means adapted to impress in said control circuit a second periodic potential of the same periodicity but displaced in phase relative to said source and having a sloping wave front superimposed on a third potential which gradually decreases as the capacitor potential increases above a preselected magnitude.

12. In combination, a capacitor, meansadapted to function as a source of periodically pulsating potential in circuit with said capacitor for supplying charging current thereto, electric discharge valve means of the arc-like type interposed between said source and capacitor for controlling each positive pulsation while the potential charge on said capacitor is below a preselected magnitude and at an instant gradually later in each succeeding positive pulsation as the capacitor` potential increases above said preselected magnitude, the rate of change of the instants at which said valve means is rendered conductive being dependent upon the rate of increase of said capacitor potential, said potential impressing means including means associated with said capacitor and eilective to amplify changes in the capacitor potential above said preselected magnitude only.

13. For use in charging a capacitor to a potential of a preselected magnitude from a sourceof periodically pulsating potential in circuit therewith, the combination comprising electric discharge valve means of the arc-like type interposed between said source and capacitor for controlling the supply of charging current to said capacitor, a control circuit connected to said valve means and arranged to render said valve means conductive when a potential greater than a predetermined critical value is impressed thereinin a positive pulsation of said source, and means adapted to impress in said control circuit a second periodic potential of the same frequency as said source and having a sloping wave front superimposed on a third potential which gradually decreases as said capacitor potential increases above a second preselected magnitude less than said iirst preselected magnitude, the magnitude of said second and third potentials being such that the resultant potential iirst rises above said critical value at substantially the same instant early in each positive pulsation while said capacitor potential is below said second preselected magnitude and at an instant gradually later in each succeeding positive pulsation as said third potential decreases, said last means including means responsive to said capacitor potential for decreasing said third potential at a rate dependent upon the rate of increase of said capacitor potential in such manner that the resultant potential does not rise above said critical value when the capacitor potential is at said first preselected magnitude.

14. Apparatus according to claim 13 in which the means responsive to said capacitor potential for decreasing said third potential comprises electronic amplifying means in circuit with said capacitor and eiective to amplify changes in the capacitor potential above said second preselected magnitude only.

15. A control system comprising a capacitor, means for charging said capacitor, a discharge circuit connected across said capacitor and including an inductive` load and normally nonconductive electric valve means interposed between said capacitor and load whereby an oscillating current tends to flow in said circuit when said valve means is conductive, and means for rendering said valve means conductive to permit a single cycle only of oscillating current to flow in said circuit.

16. For use in supplying current to a load through a magnetic core transformer having primary and secondary windings with said secondary winding being connected in circuit with saidload, the combination comprising a capacitor, means for precharging said capacitor, means including normally non-conductive electric valve means connecting said primary winding across said capacitor whereby an oscillating current tends to iiow through said primary winding when said valve means is conductive, and means for rendernglsaid valve means conductive to permit a single cycle' only `of oscillating current to flow through said primary'winding.

17. For use in supplying current to a load through a Vmagnetic core transformer Ahaving primaryV and secondary windings with said secondary winding being connected in circuit with said load, the combination comprisingv a capacitor, means for precharging said capacitor, circuit means including a pair of inversely connected electric discharge valves of the arc-like type connecting said primary Winding across said capacitor, means for rendering Vone of vsaid valves conductive to effect discharge of said capacitor through said primary winding whereby said capacitor is subsequently charged inversely, and means' operable when said one valve becomes noneconductive' for rendering the other valve conductive to effect discharge of the inverse charge on'said capacitor throughsaid primary winding.

18; For use in supplying current to a load through a magnetic core transformer having primary'and secondary windings with said secondary winding being connected. in circuit with said load, the combination comprising a capacitor, means for: precharging said capacitor, circuit means including a pair of inversely connected electric discharge valves of the arc-like type connecting said primary winding across said capacitor, means for rendering one of said valves conductive to eiiect discharge of said capacitor through said primary Winding whereby saidA capacitor is subsequently charged inversely, and means responsive to the inverse charge on said capacitor and operable when` said one valve-becomes non-conductive for rendering the other valve conductive to effect discharge of the inverse charge on said capacitor through said primary winding.

195 A control system comprising a capacitor, means for charging said capacitor, a discharge circuit" connected across said capacitor and including an inductive load and normally non-conductive electric valve means of the arc-like type interposed between said capacitor'and load and adaptedv to conductV current in either direction through said discharge circuit, whereby an oscillating current tends to flow in said circuit when said Vvalve means is conductive, and means for rendering said valve means conductive to permit a single cycle only of oscillating current to ilow in said/circuit.

20'.'1Acontrol system'comprising a capacitor, means for charging said capacitor, an inductive lo'adfcircuit means including a pair of inversely connected electric discharge valves of the arc-like type v'connecting said 'loadacross said capacitor, means for rendering one of said valves conductive to-eiectA discharge ofV said capacitor through said load,y whereby said" capacitor is subsequently charged inversely by the currentV flowing through said one valve as the result of energy released by said-inductive load as the capacitor discharge is completed, said energy being stored in said inductive load during said discharge, andmeans operable when saidone valve becomes non-conductive fory rendering the other of said valves conductive tofeffect'discharge of the inverse chargeV on said capacitor through. said inductive load.

21.` Apparatus for use in supplying current to a load comprising a capacitor, charging means connected across said capacitor and tending to supply current therethrough to charge the same Whenever the capacitor voltage is below a predetermined value, circuit means connecting said capacitor across said load to eiect discharge of said capacitor therethrough, said circuit means including valve means interposed between said capacitor and load for controlling the flow of current therebetween and impedance means in series with said valve means whereby a voltage is developed across said impedance means in response to current conducted through said valve means, means responsive to said voltage and connected to said charging means for preventing operation of said charging means only during current flow through said. valve means, and control means connested to said valve means to cause said valve means to be conductive during each of a plurality of spaced intervals.

22. Apparatus for use in supplying current to a load through a magnetic core transformer having primary and second windings with said secondary winding being connected in circuit with said load, comprising a capacitor, means connected across said capacitor to supply charging current therethrough whenever the capacitor potential is below a predetermined value, means including normally non-conductive valve means connecting said capacit'or in circuit across said primary winding whereby an oscillating current tends to flow through said'primary winding when said valve means is conductive, control means connected to said valve means for rendering the same conductive at spaced intervals to permit a full cycle of oscillating current to flow through said primary winding, impedance means in series with said valve means whereby a voltage is developed across said impedance means by current conducted through said valve means, and means responsive to'saidvoltage and connected to said charging means for preventing operation of said charging means only whilesaid valve means is conductive.

HANS KLEMPERER..

REFEEEN CTI'ED The following references are of record in the file'of this patent:

UNITED STATES PATEIITS Number Name Date 1,168,346 Thomson Jan. 18, 1916 1,769,148 Lunn July 1` 1930 2,179,105 Sidney Nov. 7, 1939 2,216,329 i Stansbury Oct. 1, 1940 2,276,796 Rogers Mar. 17, 1942 2,277,146 Roby Mar. 24, 1942 2,287,540 Vang June 23, 1942 2,287,544 Vang June 23, 1942 2,295,293 Rogers Sept. 8, 1942 2,298,570 Leathers Oct. 13, 1942 FOREIGN PATENTS Number Country Date 519,353 Great Britain Mar. 21, 1940 

